Abstract
Introduction
Total ankle replacement (TAR) has been used as a surgical intervention for arthritis since the 1970s. However, unlike clinically successful hip and knee replacements, TARs are renowned for extensive contraindications to surgery and high failure rates with an average of 83% survival at 5 years. The majority cite aseptic loosening as the reason for failure. The aim of this study wais to analyse retrieved TARs visually and through interferometry to identify potential the failure mechanisms associated with these devices.
Methods
Retrieved total ankle replacements (n=11) from consecutive revision surgeries carried out at Chapel Allerton Hospital, Leeds between August 2012 and January 2014, were collected for study at the University of Leeds, under an NRES approved procedure (09/H1307/60).
The bearing surfaces of the samples were visually inspected for evidence of damage and wear. The bearing surfaces between the tibial component and the flat surface of the polyethylene insert were then examined using a scanning white light interferometer (NP Flex, Bruker, USA). It was not possible to characterise the talar bearing surface or the inferior polyethylene surface at this stage through interferometry due to the curvature of the surface. The components were aligned and five sections on each of the surfaces measured. These sections represented; anterior-medial, anterior-lateral, posterior-medial, posterior lateral and central regions of the bearing surfaces. 3D roughness values were recorded, and the mean 3D surface roughness compared between implants. Measurements were taken on the medial and lateral aspects of the bearing surfaces to investigate whether damage was location specific. A coefficient of determination was calculated to assess the relationship between implantation time and surface roughness.
Results
Eleven total ankle replacements were received, with six right and five left TARs (Figure 1). The mean implantation time was 7.0 ± 1.4 years. Ten bearings were revised due to osteolytic cysts. Visual inspection showed evidence of multidirectional motion on both the polyethylene and metallic tibial bearing surfaces for all retrievals. Evidence of scratching, pitting, burnishing, adhesive wear was seen on all inserts. There was no evidence of gross polyethylene wear. Visual inspection indicated some metallic particles embedded in the polyethylene. The 3D surface roughness (Sa) ranged from 16.7 to 53.1nm across the tibial components. The roughness of the polyethylene surface ranged from 32.1nm to 2312.6nm (Figure 2). Such high roughness and the visible 20μm pits indicate the presence of third body particle between the articulating surfaces. There was a weak positive correlation between implantation time and surface roughness of the insert (R2=0.33) but no correlation for the tibial bearing.
Discussion
Visual inspection of the retrieved samples showed extensive surface damage to both the tibial bearing and the polyethylene insert. Presence of metallic debris embedded in the insert indicated potential for third body wear. A weak correlation indicated that bearings implanted for the longest duration had the greatest surface roughness. Whilst no clear failure mechanisms have been determined through this initial analysis, this is the first study to assess surface characteristics of failed total ankle replacements.
